Data recording apparatus

ABSTRACT

Digital data representing a compressed image is separated into priority data and normal data, and formatted so that the priority data is repeatedly recorded on a magnetic tape. The transmission rate of the digital data is compared with the recording rate on the magnetic tape to control the number of repetitions of the priority data.

This application is a continuation of application Ser. No. 08/147,579,filed Nov. 5, 1993, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a data record apparatus, and, moreparticularly, is directed to a digital video tape recorder havingspecial reproduction modes.

A digital video tape recorder is designed to record both video data andaudio data in digital form on a magnetic tape. A temporally long segmentof high-definition digital video data can be compressed before beingrecorded so as to occupy a relatively small recording capacity of amagnetic tape. Also, an analog video signal can be digitized andorthogonally transformed into frequency component coefficients, that is,digital video data also referred to herein as an advanced television(ATV) signal, by an external source, and the ATV signal can be recordedand reproduced by the digital video tape recorder.

In a special or trick reproduction mode, such as cue or review, themagnetic tape is quickly scanned in either a forward or reversedirection, and only part of the data recorded in each track of themagnetic tape is reproduced. Typically, in the special reproductionmode, conventional digital video tape recorders provide deterioratedquality reproduction of a compressed picture recorded on a magnetictape.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a datarecording apparatus which avoids the aforementioned disadvantages of theprior art.

Another object of the present invention is to record digital video dataon a magnetic tape so as to improve image reproduction in a specialreproduction mode.

Yet another object of the present invention is to record digital datarepresenting an image so that the data most essential to reproduction ofan image has the highest probability of being properly reproduced.

In accordance with an aspect of this invention, data recording apparatusseparates input data into priority data and normal data which areformatted in a predetermined format wherein the priority data isrepeated, thus producing first formatted priority data, repeat formattedpriority data and formatted normal data for recording in physical trackson a recording medium.

Since the priority data is recorded repeatedly, the probability of itsreproduction in a special reproduction mode is increased, thus improvingthe quality of an image reproduced in the special reproduction mode.

In accordance with another aspect of this invention, the recording rateof the recording medium and the transmission rate of the input data arecompared and the number of times the priority data is repeated iscontrolled as a function of the comparison.

Since the number of times the priority data is repeated depends upon thecomparison of recording rate and input transmission rate, it is possibleto prevent partial dropout of the normal data due to repetition of thepriority data when the recording rate is insufficiently high toaccommodate such repetition.

In accordance with a further aspect of this invention, the repeatformatted priority data comprises one repetition of the first formattedpriority data, but, if the comparison of the recording rate of therecording medium and the transmission rate of the input data indicatesthat the recording rate is insufficient when the priority data isrepeated, then the repeat formatted priority data comprises zerorepetitions of the first formatted priority data.

In accordance with yet another aspect of this invention, the input datacomprises digital data representing an image, such as discrete cosinetransformation coefficients. The first formatted priority data and therepeat formatted priority data are substantially at the center of eachlogical track of the predetermined format, and each logical track isrecorded in a respective physical track.

The above, and other objects, features and advantages of the presentinvention will be apparent in the following detailed description of thepreferred embodiments of the present invention when read in conjunctionwith the accompanying drawings in which corresponding parts areidentified by the same reference numeral.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of a digital video recordingand reproducing apparatus according to the present invention;

FIG. 2 illustrates a track format on a magnetic tape employed in FIG. 1;

FIG. 3 illustrates a data format of a video area shown in FIG. 2;

FIG. 4 illustrates a format for data inputted to an ATV code shown inFIG. 1;

FIGS. 5a-d are a timing chart used for explaining the operation of aninterface block shown in FIG. 1;

FIG. 6 illustrates a data format of a logical track recorded in aphysical track to which reference is made in explaining the operation ofthe apparatus shown in FIG. 1;

FIG. 7 illustrates a read out sequence for the data format shown in FIG.6;

FIG. 8 illustrates the sync blocks in the video area of the data formatshown in FIG. 6;

FIG. 9 illustrates another data format for a logical track recorded in arespective physical track;

FIG. 10 illustrates a further data format for a logical track recordedin a respective physical track; and

FIG. 11 illustrates a data format for a portion of a logical track.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention recognizes that certain of the compressed videodata are essential for adequate reproduction of an image, whereas theremainder of the compressed video data may be omitted with relativelyless effect on the quality of the reproduced image. The essentialcompressed video data are referred to herein as priority data (PD) whilethe remainder of the data are referred to as normal data (ND).

For example, in the case of an ATV signal comprising orthogonaltransform coefficients, such as discrete cosine transform coefficients,the low frequency components alone are more essential to properreproduction of an image than the high frequency components alone. Thus,the low frequency components comprise the priority data PD, while thehigh frequency components comprise the normal data ND.

In another case wherein pictures representing motion are predictivelyencoded into one of an I picture, which is coded without reference toanother picture, a P picture, which is coded with reference to atemporally preceding picture, and a B picture, which is coded withreference to a temporally preceding picture and a temporally succeedingpicture (see, for example, ISO/IEC recommendation H.26x, popularly knownas the proposed "MPEG 2" standard), the data representing I picturescomprises the priority data PD, while the data representing P and Bpictures comprises the normal data ND.

A data recording apparatus according to the present invention isoperative to repeatedly record the priority data for a picture when acomparison of the input transmission rate and maximum recording rateindicates there is adequate capacity for such repetition. The prioritydata may be repeatedly recorded on the same track or on multiple tracks.

Since the priority data is repeatedly recorded, the probability of itsreproduction during a special reproduction mode (e.g., fast playback) ishigher than for normal data. Therefore, in the present invention, theportion of the compressed data which is most essential to reproductionof a recognizable picture is most likely to be reproduced. Thus, thepresent invention improves the quality of a picture reproduced in aspecial reproduction mode, such as cue or review.

Referring now to the drawings, and in particular to FIG. 1, there isillustrated an embodiment of a data recording apparatus according to thepresent invention. The apparatus illustrated in FIG. 1 is adapted todigitally record and reproduce video data supplied thereto, andcomprises an ATV code 1, an interface block 2 including a CPU 2a, aparity generator 3, a sync and ID code generator 4, a channel encoder 5,a recording amplifier 6, switches 7, 21 and 22, a magnetic head 8, ahead amplifier/equalizer 11, a channel decoder 12, a sync and ID codedetector 13, a time base corrector (TBC) 14, an error detection andcorrection (ECC) circuit 15, and digital signal processors 23, 24.

ATV code 1 is adapted to receive input video data such as a compressedhigh-definition television signal (e.g. discrete cosine transformcoefficients) and related input audio data from a circuit, not shown, toseparate the input data into priority data PD and normal data ND, and tosupply the separated data to an interface block 2.

The interface block 2 is operative to format (pack) the priority dataand the normal data inputted from the ATV codec 1 into a data format forrecording on a magnetic tape 9 and to supply the packed data to acontact "a" of the switch 21. The interface block 2 includes CPU 2awhich functions to compare the recording rate on the magnetic tape 9with the input data transmission rate and to control the packing inaccordance with the result of this comparison. The switch 21 suppliesthe packed data to parity generator (PTG) 3.

A luminance signal Y and color difference signals P_(R), P_(B) may besupplied to digital signal processor 23 which is adapted to performanalog-to-digital conversion on these signals and also to format theminto digital video data, and to supply the digital video data to acontact "b" of the switch 21. The switch 21 may be controlled by acontrol signal (not shown) to supply to the parity generator 3 thedigital video data from the processor 23 instead of the packed data fromthe interface block 2.

The parity generator 3 serves to add parity code data to the data frominterface block 2 or processor 23, and to supply the thus augmentedpacked data to sync and ID code generator 4.

The generator 4 functions to add a sync word and ID data to the packeddata and parity code data and to supply the resulting signal to channelencoder 5.

The channel encoder 5 is operative to modulate the data supplied theretofrom the generator 4 and to apply the modulated data to recordingamplifier 6 which functions to amplify the modulated data and apply itto a contact "R" of switch 7. The switch 7 supplies the amplified datato rotary magnetic head 8 which serves to record the data in slanttracks on the magnetic tape 9.

FIG. 2 illustrates an example of a track format for a track recorded onthe magnetic tape 9. As shown, an effective area of each slant track hasa length of 16089 bytes. Margins 1 and 2, each of 455 bytes, are formedbefore and after the effective area, respectively, to accommodatevariation in positioning due to jitter.

A T-amble area of 60 bytes is formed at the beginning of the effectivearea in the forward direction of the magnetic head 8, and an ATF1 areaof 237 bytes is formed subsequent thereto. An interblock gap (IBG) and apreamble area (for convenience, preamble and postamble areas arereferred to herein simply as "amble" areas) are formed in a succeedingarea of 192 bytes. The T-amble contains a signal used for generating atiming signal which is required for reproducing the recorded data fromthe ATF1 area. The ATF1 area contains tracking control data. The amblearea following the IBG contains a signal used for generating a timingsignal required for reproducing the recorded data from a succeedingvideo area. The video area following the amble has a length of 14688bytes and is used for recording the video data.

Following the video area, in a length of 192 bytes, 18 there are formeda postamble, an interblock gap and another preamble. A succeeding areaof 288 bytes is used for recording other data, such as audio data.Thereafter, in a length of 195 bytes, there are formed a postamble, aninterblock gap and a preamble, followed by an ATF2 area formed in asucceeding area of 237 bytes for recording another tracking controlsignal.

FIG. 3 illustrates the structure of data in the video area shown in FIG.2. In this video area, the data is recorded in units of sync blocks.Here, each sync block (SB) has a length of 96 bytes. The first 2 bytesof a sync block are used for recording a sync word which serves as async signal, and the next 4 bytes are used for recording ID data toidentify the sync block. Following the ID data, video data (ATV data)may be recorded in a length of 82 bytes. The last 8 bytes of the syncblock are used for recording a horizontal parity code P1.

A vertical parity code P2 of 5 sync blocks is added to 46 sync blocks ofthe ATV data and the parity code P1 to form a unit of 51 sync blocks.Three units of 51 sync blocks are grouped and recorded as 153 syncblocks in the video area of each track. The data recording sequence isin accordance with the direction of the line shown in FIG. 3 for thesethree units.

Returning to FIG. 1, it will be seen that, during a playback mode, themagnetic head 8 applies data reproduced from the magnetic tape 9 to acontact P of the switch 7 and thence to head amplifier/equalizer 11which functions to compensate higher frequency components of the inputdata and to supply compensated data to channel decoder 12.

The channel decoder 12 functions to demodulate the compensated data andto supply demodulated data to sync and ID code detector 13 which isadapted to detect sync words and ID data present in the demodulated dataand to supply the detected data with the demodulated data (video oraudio data) to time base corrector (TBC) 14.

The TBC 14 is operative to correct the time base of the demodulatedvideo or audio data and to supply time base corrected data to ECCcircuit 15 which functions to detect and correct errors in thereproduced data and to apply the corrected data to switch 22.

The switch 22 applies the corrected data to the interface block 2through a contact "a". The interface block 2 is further operative todeformat (depack) the reproduced data and to apply the depacked data tothe ATV codec 1.

Alternatively, a control signal (not shown) may cause the switch 22 toapply the corrected data from the ECC circuit to a contact "b" which inturn applies the corrected data to digital signal processor 24 that isadapted to reformat the corrected data and perform digital-to-analogconversion thereof to produce a luminance signal Y and color differencesignals P_(R), P_(B). These analog signals may be supplied to anothersystem (not shown).

A recording operation of the embodiment of the present invention shownin FIG. 1 will now be described below.

FIG. 4 shows the format of cells of ATV data received by the ATV codec 1during recording. Each cell has a total length of 150 bytes and includessync data, header data, video or audio data (as the case may be) andparity data. The sync data are a sync signal for separating the cells.The header data includes ID data for identifying the cell. The video oraudio data are recorded in the video or audio data areas of a track. Theparity data are a code for detecting and correcting errors in the videoor audio data.

The ATV codec 1 separates the input ATV data of each cell into prioritydata PD and normal data ND, and, as shown in the timing diagrams ofFIGS. 5(a) and 5(c), supplies the separated data in units of, e.g., 150bytes, comprising either priority data or normal data, to the interfaceblock 2.

The interface block 2 formats the data of each cell into multiple syncblocks in the format of FIG. 3. Thus, as shown in FIGS. 5(b) and 5(d),the priority data PD and the normal data ND are respectively formattedinto sync blocks each having 82 bytes.

The interface block 2 temporarily stores an amount of input video datacorresponding to one track, that is, 3×2 unused sync blocks followed by3×44 sync blocks of video data, as shown in FIG. 6. The interface block2 sequentially reads out the temporarily stored track of data in unitsof 82 byte sync blocks in the order indicated by numbers 0, 1, 2, 3, 4 .. . in FIG. 7.

The data read out from the interface block 2 are supplied via thecontact "a" of the switch 21 to the parity generator 3, which calculatesthe horizontal parity code C1, also referred to herein as parity dataP1, and the vertical parity code C2, also referred to herein as paritydata P2, for the input data and appends such parity codes to the readout data. The video and parity code data are supplied to the sync and IDcode generator 4 which adds sync words and ID data to produce recordingdata in the format shown in FIG. 6.

The recording data are supplied to the channel encoder 5 for modulation.The modulated data produced by the channel encoder 5 are supplied to therecording amplifier 6 to be amplified, and then the amplified data aresupplied via the contact R of the switch 7 to the magnetic head 8, whichrecords the data on each track of the magnetic tape 9.

The CPU 2a incorporated in the interface block 2 controls the formattingof the cells into sync blocks comprising logical tracks which arerecorded in respective physical tracks on the magnetic tape 9 so thatthe priority data PD is positioned substantially at the center of eachphysical track on the magnetic tape.

The CPU 2a also compares the input data transmission rate with therecording rate on the magnetic tape 9 to decide whether the entirety ofthe input data can be temporarily stored without overflow and recordedon the magnetic tape 9 even if the priority data PD is repeated. If therecording rate is sufficiently high in comparison with the input datatransmission rate, the priority data PD is repeated. If the recordingrate on the magnetic tape 9 is not sufficiently high, the CPU 2a formatsthe priority data only once as original data and not again as repeatdata.

More specifically, as shown in FIG. 8, at the beginning of the videoarea of 153 sync blocks on each slant track, the CPU 2a formats blankdata in a length of 6 sync blocks, then formats normal data as formattednormal data ND in a length of 44 sync blocks. Next, the CPU 2a formatsthe priority data PD as original formatted priority data in a length of22 sync blocks and, assuming a sufficiently high recording rate, asrepeat formatted priority data in a succeeding area of 22 sync blocks.Thus, in the present embodiment, the priority data PD is recorded twice,once as original data and once as repeat data. Subsequently, the CPU 2aformats normal data ND in a length of 44 sync blocks. As mentioned, thedata in the respective sync blocks comprise a two-byte sync word, fourbytes of ID data, 82 bytes of ATV data (video data) and an eight byteparity code.

Also as shown in FIG. 8, the vertical parity code C2 is placed in alength of 15 sync blocks by the parity generator 3.

In another recording operation, the processor 23 formats a luminancesignal Y and color difference signals P_(R), P_(B) into digital videodata in the format shown in FIG. 3. This digital video data is suppliedthrough the contact "b" of switch 21 to the parity generator 3 to berecorded on the magnetic tape 9 in the manner generally described above.

A reproducing operation of the embodiment of the present invention shownin FIG. 1 will now be described below.

Data reproduced from the magnetic tape 9 by the magnetic head 8 isinputted via the contact P of the switch 7 to the headamplifier/equalizer 11 where the higher-frequency components arecompensated. The compensated data are supplied to the channel decoder 12to be demodulated. The demodulated data are applied to the sync-IDdetector 13 for detection of the sync word and the ID data in each syncblock, and thence to the TBC 14.

The corrected data produced by the TBC 14 are supplied to the ECCcircuit 15 for error detection and correction. The corrected data isapplied via the contact "a" of the switch 22 to the interface block 2.

The interface block 2 depacks the reproduced data in units of 82 bytesinto data in units of 148 bytes. In this depacking, the data reproducedfrom the center area of each track, namely, two lengths of 22 syncblocks, are considered to be the priority data PD. Since the prioritydata is duplicated, the interface block 2 selects only one length of 22sync blocks of the reproduced data as the priority data. The datareproduced from each area of 44 sync blocks before and after thepriority data PD are processed as the normal data ND. The depacked dataare outputted to the ATV codec 1.

The ATV codec 1 converts the priority data PD and normal data NDsupplied thereto into cells in the format of FIG. 4 and delivers itsoutput for use by another system, not shown. Data of multiple syncblocks are formed into each cell.

In another reproducing operation, the corrected data is applied throughthe contact "b" of switch 22 to the processor 23 which converts thecorrected digital video data into a luminance signal Y and colordifference signals P_(R), P_(B).

In the embodiment described above, the priority data PD is positioned atthe center of each track. However, the data arrangement in a logicaltrack may be modified so that, as shown in FIG. 9, in a record (orphysical) track the priority data PD is recorded at both ends of thetrack, while the normal data ND is recorded at the center of the track.

Additionally, when the video data of one frame is processed in a unit ofplural tracks (e.g., four tracks), the priority data PD may berepeatedly recorded at predetermined positions on a plurality of tracksas shown in FIG. 10.

A further modification is possible as shown in FIG. 11 wherein formattedgroups are recorded sequentially on each record track. Each formattedgroup contains a predetermined number of sync blocks of priority data PDfollowed by a predetermined number of sync blocks of normal data ND. Ineach formatted group, the sync blocks of priority data may includeoriginal or first priority data, and repetitions of the first prioritydata. For example, FIG. 11 shows first formatted priority data followedby repeat formatted priority data in each formatted group.

Although an illustrative embodiment of the present invention, andvarious modifications thereof, have been described in detail herein withreference to the accompanying drawings, it is to be understood that theinvention is not limited to this precise embodiment and the describedmodifications, and that various changes and further modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the invention as defined in the appended claims.

What is claimed is:
 1. A data recording apparatus comprising:means forseparating input data into priority data and normal data, said inputdata having a transmission rate; means for formatting said priority dataand said normal data in a predetermined format in which said prioritydata is repeated to produce first formatted priority data, repeatformatted priority data and formatted normal data; means for recordingsaid first formatted priority data, said repeat formatted priority dataand said formatted normal data in record tracks on a recording medium,said means for recording having a recording rate; and means forcomparing the recording rate and the transmission rate and forcontrolling the number of times said priority data is repeated by saidmeans for formatting as a function of the comparison.
 2. The apparatusaccording to claim 1, wherein said number of times said priority data isrepeated is zero when said comparison indicates said recording rate isinsufficient to record said repeat formatted priority data.